Field of the Invention
The present invention relates to an image sensor and an image capturing apparatus.
Description of the Related Art
As a focus detection method performed by an image capturing apparatus, an on-imaging surface phase difference method is used in which focus detection by a phase difference method is performed using focus detection pixels formed in an image sensor.
U.S. Pat. No. 4,410,804 discloses an image capturing apparatus using a two-dimensional image sensor in which one microlens and a plurality of photoelectric conversion units are formed in each pixel. The plurality of photoelectric conversion units are configured to receive light components that have passed through different regions of the exit pupil of an imaging lens via one microlens, thereby dividing the pupil. A correlation amount is calculated from focus detection signals output from pixels (focus detection pixels) each including a plurality of photoelectric conversion units, and an image shift amount is obtained from the correlation amount, thereby performing focus detection by the phase difference method. Further, Japanese Patent Laid-Open No. 2001-083407 discloses generating an image signal by adding focus detection signals output from a plurality of photoelectric conversion units for each pixel.
Japanese Patent Laid-Open No. 2000-156823 discloses an image capturing apparatus in which pairs of focus detection pixels are partially arranged in a two-dimensional image sensor formed from a plurality of imaging pixels. The pairs of focus detection pixels are configured to receive light components from different regions of the exit pupil of an imaging lens via a light shielding layer having openings, thereby dividing the pupil. An image signal is acquired by imaging pixels arranged on most part of the two-dimensional image sensor. A correlation amount is calculated from focus detection signals of the partially arranged focus detection pixels, and an image shift amount is obtained from the calculated correlation amount, thereby performing focus detection by the phase difference method, as disclosed.
In focus detection using the on-imaging surface phase difference method, the defocus direction and the defocus amount can simultaneously be detected by focus detection pixels formed in an image sensor. It is therefore possible to perform focus control at a high speed.
However, in the on-imaging surface phase difference method, there is a problem in that, when a variation range of an incident angle of light from an imaging lens (imaging optical system) on an image sensor at a peripheral portion is large, a pupil deviation between an entrance pupil of a sensor and an exit pupil of the imaging lens is large, and the base line length is not secured, and consequently there is a case in which the focus detection quality by the on-imaging surface phase difference method deteriorates.